1. Field of the Invention
This invention relates in general to gerotor-type motors and more particularly to such motors capable of operating at two speeds.
2. Description of the Prior Art
Gerotor type pumps and motors are well known to those in the pump and motor art. They include a power element which has a lobed set of gears which, when rotating, form increasing and decreasing volume cavities therebetween. Gerotor type pumps and motors are shown in U.S. Pat. Nos. 4,501,536; 4,545,748; and 4,563,136.
Among the various gerotor-type motors are motors capable of operating at two speeds and torques at a given flow and pressure in the driving fluid. This allows both high speed, low torque and low speed, high torque motor operation. Generally these motors are constructed to operate at two speeds in one of two ways. In the first two speed construction the motor has a single power element with a commutator and valve capable of converting selected motor chambers to pumping chambers and vice versa. Examples of this type of two speed construction are shown in U.S. Pat. Nos. 3,778,198; 4,480,971; and 4,715,798.
These motors suffer from cavitation problems in the high speed mode. In order for these motors to operate efficiently in the low speed mode, the power element must be designed in such a manner that the conversion of motor chambers to pumping chambers in the high speed mode causes the element to rotate fast enough that cavitation occurs in the fluid. This cavitation causes damage to the motor. In addition, this construction requires an external pilot valve and a pressurized fluid source for shifting between speeds.
The other two speed construction for gerotor-type motors requires two power elements and an external valve for shifting. In the low speed mode the power elements are connected in parallel while in the high speed mode the power elements are connected in series. While this construction does not suffer from the problem of cavitation, it does have a problem with pressure drop. In this construction, the valves which allow the power elements to be switched between parallel and series operation are located outside the motor and are connected to the motor by hoses. This arrangement results in a long travel path and narrow passages for the fluid which powers the power elements.
It is accordingly an object of the present invention to provide a two speed gerotor-type motor which is improved in its ability to operate efficiently at two speeds without cavitation or excess noise and with less pressure drop in the power fluid than in prior art constructions.
It is also an object of the present invention to provide a two speed gerotor-type motor with an improved structure. Still further it is an object to provide such a motor which is compact and reliable.
Another object of the present invention is to provide a two speed construction with a remotely operated valve system integral to the motor. Particularly, it is an object to provide such a system which uses a motor drive fluid for all shifting in order to allow the use of solenoid, manual or automatic control.
Still another object of the present invention is to provide a differential two speed motor option with two independent output shafts capable of independent operation while in parallel mode and locked by fluid pressure when in series mode.